People will always try to find good uses. I could see a Lum Berry set make for a decent status absorber which can then abuse Magician for example.
The best pokemon to compare this to is Gengar I think. Both have great special attack and an exhaustive support movepool.
Gengar 60/65/60/130/75/110
Resist: x0 Normal, x.5 Grass, x0 Fighting, x.25 Poison, x.5 Bug, x.5 Fairy, x0 Ground (Ability)
Weakness: Psychic, Ghost, Dark
Hoopa 80/110/60/150/130/70
Resist: x0 Normal, x0 Fighting, x.5 Poison, x.5 Psychic, x4 Ghost, x4 Dark
We often forget how frail Gengar is at times because it is consistently one of the best and commonly seen OU pokemon, but as we can see, Gengar has to abuse those immunities and a few good special resists if it wants to switch into anything. And added ground immunity and Gengars fantastic speed are its biggest assets allowing it to really abuse that movepool of its.
Statwise of course, Hoopa is a monster in comparison, having effectively double the SpD when you factor in the extra 20 in HP as well as the option to invest in those stats. And those attack stats are nothing to sneeze at.
Gengar Timid 252 SpA / 252 Spd
262/149/156/359/186/350
Hoopa Modest 252 HP / 252 SpD
364/230/156/370/359/176
With a Modest nature and 0 investment you will still have a higher SpA stat than Gengar, albeit by 10/11 points. Meanwhile you get a spectacular SpD total roughly doubly effective.
+1 4 SpA Suicune Scald vs. 4 HP / 0 SpD Gengar: 151-178 (57.6 - 67.9%) -- guaranteed 2HKO after Black Sludge recovery
+1 4 SpA Suicune Scald vs. 252 HP / 252 SpD Hoopa: 78-93 (21.4 - 25.5%) -- 0.3% chance to 4HKO
Gengar dies to Pursuit and Knock Off in single hits as is, no different than Hoopa. But Hoopa's ability to take neutral hits is in a different league. Naturally though, Gengar's speed is so fantastic that it can often 2HKO without getting touched in return, but it does have a smaller margin for error. Hoopa is a pretty good check to the Lati twins. The SpD spread can't be 2HKO, even by Psyshock, and STAB Shadow Ball has over 60% chance to OHKO Latios after rocks.
Now don't think I'm saying Hoopa is surefire OU. I'm just trying to think outside the box and show Hoopa in a different context, possibly try to spark some ingenuity and creative thinking. Hoopa has a pretty good framework to be usable, but it really is its speed that is the nail in the coffin more than anything else. Its 4x weaknesses are rendered moot as with its defense stat it would still die horribly if it were only 2x weak.